1 Field of the Invention
This invention relates to a power system for use in driving a plurality of electric devices such as a tape recorder, radio tuner, and television tuner and, more particularly, to a switching system for selectively connecting such electric devices to a power source.
2. Description of the Prior Art
Normally, electric devices such as tape recorders, radio tuners, television tuners or the like equipped on a road vehicle are powered by the vehicle battery which has a small capacity and is not intended to simultaneously power each such device. Accordingly, it is a common practice to use a switching circuit arranged to prohibit simultaneous operation of two or more of the electric devices.
For example, a switching circuit has been proposed which can selectively connect the car battery to one of the electric devices according to its priority level predetermined therefor according to frequency of use or other criteria. With this prior art switching circuit, any device with a lower priority cannot be powered while an electric device with a higher priority is in use. However, such a conventional switching circuit has had several disadvantages. First, two operations are required to operate the lower priority electric device while the higher priority electric device is in use. That is, the lower priority electric device cannot be placed into operation without turning on the switch associated therewith after turning off the switch associated with the higher priority electric device. Second, although it is possible to operate the higher priority electric device when the lower priority electric device is in use only by turning on the switch associated with the higher priority electric device, the lower priority electric device will automatically operate unnecessarily after the switch associated with the higher priority electric device is turned off if the switch associated with the lower priority electric device remains on.
The present invention provides a switching system which can prevent simultaneous connection of two or more electric devices to a power source but permits connection of one of the electric devices to the power source with another electric device remaining coupled to the power source when the first electric device is in a predetermined mode of operation.